The invention relates to a controlled release urea-formaldehyde liquid fertilizer resin having a nitrogen level of at least about 28 wt % and a method of preparing the resin.
Urea-formaldehyde based liquid fertilizers have been used for some time to provide nitrogen to the soil. In addition to nitrogen, phosphorous and potassium are considered major nutrients essential for plant growth. Over time, these major nutrients become deficient in the soil because plants use relatively large amounts of such nutrients. In addition to the major nutrients, secondary and micro-nutrients are also needed, but are usually deficient less often and are used in smaller amounts in fertilizer formulations. It is desirable to have a urea-formaldehyde base resin that contains the necessary nitrogen component, is stable, and capable of solubilizing different levels of phosphorus, potassium, and micro-nutrients from various sources while maintaining stability.
In the past, long term stability of high nitrogen (around 30%) liquid urea-formaldehyde fertilizers was achieved by forming either a high percentage (more than 30%) of cyclic triazone structures or by condensing the urea-formaldehyde resin into small urea-formaldehyde polymer chains.
Several patents issued to Hawkins describe the preparation of urea-formaldehyde resins having high triazone contents. U.S. Pat. No. 4,554,005 describes a reaction that produces at least about 30% triazone and has a preferred urea, formaldehyde, ammonia ratio of 1.2/1.0/0.28. Hawkins further describes preparing 30% nitrogen, liquid UF resin (containing 50% controlled release and 50% quick release nitrogen (50/50)) by starting with a 28% nitrogen liquid UF resin which is 70% controlled release and 30% quick release (70/30) and adding urea. There is only one (70/30) resin known in the industry which can be used to consistently produce a clear, storage-stable 50/50 resin containing 30% nitrogen by fortification with urea. This product is currently produced by Tessenderlo Kerley Inc. and marketed as N-SURE(copyright).
U.S. Pat. No. 4,599,102 describes a reaction that produces at least about 30% triazone and has a urea, formaldehyde, ammonia ratio of 1.2/1.0/0.5. Both of these resins have a high percentage of ammonia. U.S. Pat. No. 4,776,879 describes a reaction that produces at least about 75% triazone in water insoluble forms. This material is then crystallized out and re-dissolved at low solids levels for use. U.S. Pat. No. 4,778,510 describes a reaction that produces at least about 48% triazone. The nitrogen is the useful part of the fertilizer to the plant and thus the higher the percentage of nitrogen, the more efficient the fertilizer.
Other patents describe condensing the resin into small chains. U.S. Pat. No. 4,781,749 to Moore reacts 1.5 to 2.5 mols formaldehyde per mole of urea in the presence of ammonium compounds such as ammonia. This initial mole ratio is below the initial mole ratio of 5 to 4 mols formaldehyde per mole of urea of the present invention. The pH is maintained at near neutral conditions (6.9-8.5) throughout the reaction. Condensed UF chains have lower solubility than methylolated ureas and could continue to advance, leading to extremely slow release.
U.S. Pat. No. 3,970,625 to Moore et al. describes a process for preparing urea-formaldehyde concentrates for use as slow release fertilizers or as adhesives. Urea and formaldehyde are mixed in a molar ratio of 1/4.4-7.3 with no more than 0.015 wt. % of ammonia present in the urea. The pH is adjusted to 8.8-9.5 and the mixture is heated to 50-60xc2x0 C. for 30-60 minutes. Thereafter, water is removed by distillation under reduced pressure until solids comprise 60-90% of the remaining residue. For producing fertilizers, the residue is heated for another 48 hours at a temperature of 45-50xc2x0 C.
U.S. Pat. No. 5,449,394 to Moore relates to liquid non-polymeric controlled-release nitrogen plant food compositions containing the condensation products of one part ammonia, two parts urea and three parts formaldehyde at a base buffered pH slightly above 7. The reaction is accomplished at a temperature of about 100xc2x0 C. for 30-300 minutes. Water may be removed by evaporation until the nitrogen content of the formulation is between 20 and 30%. The solution is cooled before polymerization producing chains of more than 3 urea moieties can occur.
U.S. Pat. No. 3,677,736 to Formaini describes a process for manufacturing a liquid fertilizer suspension by preparing an aqueous mixture of urea and formaldehyde having a urea to formaldehyde ratio of 1-2:1 (F:U ratio of 0.5-1:1). Ammonia is then added in an amount of 0.3-6% by weight and the mixture is heated while maintaining the pH in the range of above 7. After heating, the resulting reaction product is diluted with water and an acidic material is added to adjust the pH to 1-4, then the solution is acidified and reheated. The pH is then adjusted to a pH of between 5 and 8.
It is desirable to make a stable urea-formaldehyde resin suitable for fertilizer use that uses significantly less triazone and no acid condensation, and has a higher nitrogen concentration than prior art resins. It is also desirable to have a resin that contains at least 50% controlled release nitrogen and will provide stable solutions with phosphate and potassium salts and other micro-nutrients.
The invention is directed to a method of making a stable urea-formaldehyde resin suitable for fertilizer use which uses significantly less triazone than the Hawkins"" process and no condensation reaction like the Moore processes, has a high nitrogen concentration, and yet is very stable, for instance, for at least two months at 25xc2x0 C.
In particular, the invention is directed to a urea-formaldehyde liquid resin prepared by the method comprising:
1) combining formaldehyde, urea, and ammonia in a basic solution at a formaldehyde/urea/ammonia ratio of about 0.6-1/1/0.25-0.35;
2) heating the solution to about 80xc2x0 C. to about 95xc2x0 C., while maintaining a pH of at least 7 for at least 45 minutes;
3) cooling the solution to less than about 50xc2x0 C., and adjusting the pH to about 9.0 to about 10.5;
wherein the nitrogen content of the resin is at least about 28 wt % based on 100% resin solids with about 50 to about 60 wt % of the nitrogen being controlled release and about 40 to about 50 wt % of the nitrogen being quick release.
The fertilizer resin exhibits superior miscibility with various phosphate, potassium, and micro-nutrient sources while maintaining water clarity and excellent storage stability.
The invention is directed to a controlled release liquid urea-formaldehyde fertilizer prepared from a solution prepared by the reaction of formaldehyde, urea, and ammonia.
The nitrogen level of the urea-formaldehyde resin is at least about 28%, preferably at least about 30 wt %, and more preferably between about 30 and 32 wt %. The final mole ratio of formaldehyde:urea:ammonia is about 0.6-1:1:0.25-0.35. The nitrogen content is about 50 wt % to about 60 wt % controlled release, preferably about 55 to about 60 wt % and about 40 to about 50 wt % quick release, preferably about 40 wt % to about 45 wt %.
Quick release nitrogen refers to free urea. Controlled release nitrogen refers to substituted urea. Structure I below is a free urea and II-VII are each a substituted urea with IV-VII representing various triazones. 
The fertilizer of the invention has the ability to solubilize varying concentrations of potassium and phosphate salts while maintaining excellent storage stability. The resin can be prepared in a reactor without isolation and eliminates the need for the end user to add or mix in urea. No acid condensation steps are required in the instant invention.
In accordance with the process of the invention:
Formaldehyde, urea, and ammonia are combined in a basic solution at a formaldehyde/urea/ammonia ratio of about 0.6-1/1/0.25-0.35, preferably about 0.7-0.9/1/0.25-0.3, and most preferably about 0.8/1/0.27. All or most of the water present comes from UFC and the ammonia source. Water may be added at the completion of the cook to adjust nitrogen content.
The solution is heated to about 80xc2x0 C. to about 95xc2x0 C., preferably about 85xc2x0 C. to about 90xc2x0 C., and held for at least about 45 minutes, preferably about 45 to about 120 minutes, more preferably about 60 to about 75 minutes, to ensure triazone formation and complete reaction of formaldehyde. Approximately 14 to 20% of the urea is in the form of triazone, preferably about 17 to about 20%. The pH level solution is at least 7, preferably about 7.5 to about 10.5, more preferably about 8.5 to about 9.5.
The solution is cooled to less than about 50xc2x0 C., preferably about ambient temperature and the pH is adjusted to about 9 to about 10.5, preferably about 9.5 to about 10.
The process of the invention provides a urea-formaldehyde resin in which the triazone content, mono-, di-, and tri-substituted urea has been optimized for maximum stability and compatibility with producing stable blends with various phosphate and potassium salts and other micro-nutrients.
The pH may be maintained or adjusted by adding a compound, such as triethanolamine, borax, sodium or potassium bicarbonate, or sodium or potassium carbonate, preferably triethanolamine, at the start of the batch that will buffer the pH of the batch at the desired pH level. Alternatively, the pH may be maintained by addition of any suitable base during the reaction. While any base can be used to increase the pH of the reaction mix, preferably alkali metal hydroxides are used such as potassium hydroxide, lithium hydroxide, and sodium hydroxide.
Skilled practitioners recognize that the reactants are commercially available in many forms. Any form which can react with the other reactants and which does not introduce extraneous moieties deleterious to the desired reaction and reaction product can be used in the preparation of the urea-formaldehyde resin of the invention.
Formaldehyde is available in many forms. Paraform (solid, polymerized formaldehyde) and formalin solutions (aqueous solutions of formaldehyde, sometimes with methanol, in 37 percent, 44 percent, or 50 percent formaldehyde concentrations) are commonly used forms. Formaldehyde also is available as a gas. Any of these forms is suitable for use in the practice of the invention. Typically, formalin solutions are preferred as the formaldehyde source. In addition, formaldehyde may be substituted in part or in whole with substituted aldehydes such as acetaldehyde and or propylaldehyde. Glyoxal may also be used in place of formaldehyde as may other aldehydes not listed. It is to be recognized that the aldehyde is dissolved (solubilized) in water or other appropriate non-reactive organic of any desired or conventional nature, known in the art.
Similarly, urea is available in many forms. Solid urea, such as prill, and urea solutions, typically aqueous solutions, are commonly available. Further, urea may be combined with another moiety, most typically formaldehyde and urea-formaldehyde, often in aqueous solution. Any form of urea or urea in combination with formaldehyde is suitable for use in the practice of the invention. Both urea prill and combined urea-formaldehyde products are preferred, such as Urea Formaldehyde Concentrate or UFC 85. These types of products are disclosed in, for example, U.S. Pat. Nos. 5,362,842 and 5,389,716.
Commercially available aqueous formaldehyde and urea-containing solutions are preferred. Such solutions typically contain between about 60 and 25 percent formaldehyde and urea, respectively.
A solution having 35% ammonia can be used providing stability and control problems can be overcome. An aqueous solution containing about 28% ammonia is particularly preferred. Anhydrous ammonia may also be used.
In substitution in part or in whole, for the ammonia, any primary amine or substituted primary amine may be used such as methyl amine, monomethanol amine, amino propanol and the like. Further, difunctional amines may be used such as ethylene diamine or any combination of organic amines provided that one primary amine group is available to form the triazone ring. The reaction rates are much faster and more straight forward. Another reactant of interest is sodium sulfamate to make the cyclic urea sulfonate.
In a preferred embodiment of the invention, the urea-formaldehyde liquid fertilizer resins have a free urea content of 45-55 wt %, a cyclic urea content of 14-20 wt %, a monomethylol urea content of 25-35 wt % and a di/trimethylurea content of 5-15 wt % based on the urea-formaldehyde resin and, based on a 65-75 wt % urea solution, a free urea content of 31.5-38.5 wt %, a cyclic urea content of 9.8-14 wt %, a monomethylol urea content of 17.5-24.5 wt % and a di/trimethylurea content of 3.5-10.5 wt % wherein the rest of the solution is composed of water, ammonia, and formaldehyde.
The urea-formaldehyde liquid resin of the invention may then be used as a fertilizer. Other additives may be mixed into the liquid fertilizer prior to use such as any of a wide variety of well-known inorganic fertilizer nutrients based on phosphorous and potassium. Suitable nutrients may be obtained from K-Fol, 0-40-53, which is a solution containing 40% phosphate and 53% potassium. A suspension aid may be used such as a humate solution such as K-Tionic. K-Fol and K-Tionic are manufactured/distributed by GBS Biosciences, LLC. Edinburgh, Tex.
Pesticides may also be mixed in, e.g., to control weeds and kill insect larvae. Suitable additives are within the skill of the art.